Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $24.80   5.837%   $26.2476   $26.25   $26.25   $26.20  
  Purchase #2 $106.74   11.549%   $119.0674   $119.07   $119.05   $119.10  
  Purchase #3 $47.60   5.160%   $50.0562   $50.06   $50.05   $50.10  
  Purchase #4 $45.71   4.868%   $47.9352   $47.94   $47.95   $47.90  
  Purchase #5 $160.92   10.675%   $178.0982   $178.10   $178.10   $178.10  
  Purchase #6 $57.33   12.141%   $64.2904   $64.29   $64.30   $64.30  
  Purchase #7 $213.25   13.463%   $241.9598   $241.96   $241.95   $242.00  
  7 purchase totals = $656.35       $727.6548   $727.67   $727.65   $727.70